Similar color detection in Python

Question

Given a color either in RGB or Hex, how do I find colors that are similar to it? By similar I mean they should be distinguishable by small values.

Answer 1

The RGB color space is device dependent and not perceptually uniform. If you intend to measure color similarities, you should transform first the RGB values into a device-independent and more perceptually uniform color space, for example CIELAB. Then you can measure the color differences through a proper similarity metric, like Lab Delta E.

Demo

Consider this image:

Let us assume that your reference colors are a shade of green and a shade of magenta, whose RGB values are for example [0, 160, 0] and [120, 0, 140]. The following snippet identifies those image pixels whose Delta E with respect to the reference colors is lower than a certain threshold (15 and 20, respectively).

import numpy as np
from skimage import io
from skimage.color import rgb2lab, deltaE_cie76

rgb = io.imread('https://i.stack.imgur.com/npnrv.png')
lab = rgb2lab(rgb)

green = [0, 160, 0]
magenta = [120, 0, 140]

threshold_green = 15    
threshold_magenta = 20    

green_3d = np.uint8(np.asarray([[green]]))
magenta_3d = np.uint8(np.asarray([[magenta]]))

dE_green = deltaE_cie76(rgb2lab(green_3d), lab)
dE_magenta = deltaE_cie76(rgb2lab(magenta_3d), lab)

rgb[dE_green < threshold_green] = green_3d
rgb[dE_magenta < threshold_magenta] = magenta_3d
io.imshow(rgb)